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Curious to hear from someone who may know more about HVAC than me: Why don’t subway stations simply install giant industrial mini-spit-style air conditioners i

Curious to hear from someone who may know more about HVAC than me: Why don’t subway stations simply install giant industrial mini-spit-style air conditioners in these stations? It doesn’t seem particularly hard to rout a few dozen tubes of coolant down to a station while keeping the compressor and expelling heat outside.

Alex3917 8y ago
> It doesn’t seem particularly hard to rout a few dozen tubes of coolant down to a station while keeping the compressor and expelling heat outside. It's hard when you're spending $90.4M to install 3 elevators. That said, while mostly it's just an annoyance, the heat really is a hazard at a handful of stations; people are regularly blacking out at union square while waiting for the L.
- awiesenhofer 8y ago
  Any ideas why its so expensive? For 90m you could get a whole new tram line...
tomarr 8y ago
The ducts get very large, so trying to fit them in existing infrastructure is a big challenge. Also consider that much of original 'spare' space has been repurposed for additional systems (CCTV, PA, additional power etc). It's different for new infrastructure where this can be allocated more readily at a smaller marginal cost.
amarshall 8y ago
Air conditioning in a large, unenclosed space is quite costly and inefficient. Stations typically have passive ventilation (in most NYC stations along most of the length of the platform, plus entrances). And then there’s the massive tunnel that lies between stations. The London Underground (which is referenced in the article) did a lot of things, but they didn’t try to air condition the stations. They did in-station air circulation, active ventilation from surface air, heat exchange cooling from existing cool water sources, and heat re-capture to heat homes. Then, of course, more specific to NYC, is that it’s more worthwhile presently to spend money on making the trains run more smoothly (whereby passengers will spend less time in the station), as the system has major issues there (and not enough money as-is).
zkms 8y ago
> giant industrial mini-spit-style air conditioners With mini-splits, the piping carries refrigerant (which actively participates in the thermodynamic cycle, rather than just being a simple heat exchange fluid), but the problem is that you need quite exacting standards for the air-tightness of the system, the materials used, and the pressures can be quite high. Also, combining multiple refrigeration units is...tricky. Usually the way industrial-scale cooling/refrigeration is done is with devices called "chillers", in which all the refrigerant is entirely captive inside the chiller unit, and all you do with the chiller is hook it up to a supply of cooling water to dump heat into (or directly expose it to outside air), and you feed it water that it will cool down. Also give it an electricity hookup. You then use the chilled water to cool down whatever you want. The advantage is that you've reduced the problem to just moving around water -- which isn't a mixture of multiple exotic fluorocarbons and compressor lube oil with special handling needs, it's just bloody water (don't drink it though, there's all sorts of dissolved metals and antifreeze and biocides). Modern chillers are wonders of engineering, some even have active magnetic bearings that levitate the moving parts with fancy diagnostic/instrumentation systems that can tell you, to the micrometer, the position of the levitated shaft (not kidding, http://cgproducts.johnsoncontrols.com/yorkdoc/160.78-o2.pdf http://cgproducts.johnsoncontrols.com/yorkdoc/160.78-o2.pdf page 37). But yes, it's absolutely possible to do what you suggest, it's just that you'd end up moving chilled water and not refrigerant.

Alex3917 8y ago

> It doesn’t seem particularly hard to rout a few dozen tubes of coolant down to a station while keeping the compressor and expelling heat outside. It's hard when you're spending $90.4M to install 3 elevators. That said, while mostly it's just an annoyance, the heat really is a hazard at a handful of stations; people are regularly blacking out at union square while waiting for the L.

awiesenhofer 8y ago
Any ideas why its so expensive? For 90m you could get a whole new tram line...

tomarr 8y ago

The ducts get very large, so trying to fit them in existing infrastructure is a big challenge. Also consider that much of original 'spare' space has been repurposed for additional systems (CCTV, PA, additional power etc). It's different for new infrastructure where this can be allocated more readily at a smaller marginal cost.

amarshall 8y ago

Air conditioning in a large, unenclosed space is quite costly and inefficient. Stations typically have passive ventilation (in most NYC stations along most of the length of the platform, plus entrances). And then there’s the massive tunnel that lies between stations. The London Underground (which is referenced in the article) did a lot of things, but they didn’t try to air condition the stations. They did in-station air circulation, active ventilation from surface air, heat exchange cooling from existing cool water sources, and heat re-capture to heat homes. Then, of course, more specific to NYC, is that it’s more worthwhile presently to spend money on making the trains run more smoothly (whereby passengers will spend less time in the station), as the system has major issues there (and not enough money as-is).

zkms 8y ago

> giant industrial mini-spit-style air conditioners With mini-splits, the piping carries refrigerant (which actively participates in the thermodynamic cycle, rather than just being a simple heat exchange fluid), but the problem is that you need quite exacting standards for the air-tightness of the system, the materials used, and the pressures can be quite high. Also, combining multiple refrigeration units is...tricky. Usually the way industrial-scale cooling/refrigeration is done is with devices called "chillers", in which all the refrigerant is entirely captive inside the chiller unit, and all you do with the chiller is hook it up to a supply of cooling water to dump heat into (or directly expose it to outside air), and you feed it water that it will cool down. Also give it an electricity hookup. You then use the chilled water to cool down whatever you want. The advantage is that you've reduced the problem to just moving around water -- which isn't a mixture of multiple exotic fluorocarbons and compressor lube oil with special handling needs, it's just bloody water (don't drink it though, there's all sorts of dissolved metals and antifreeze and biocides). Modern chillers are wonders of engineering, some even have active magnetic bearings that levitate the moving parts with fancy diagnostic/instrumentation systems that can tell you, to the micrometer, the position of the levitated shaft (not kidding, http://cgproducts.johnsoncontrols.com/yorkdoc/160.78-o2.pdf http://cgproducts.johnsoncontrols.com/yorkdoc/160.78-o2.pdf page 37). But yes, it's absolutely possible to do what you suggest, it's just that you'd end up moving chilled water and not refrigerant.